The invention relates to the fields of vesicles and molecular transport.
The advent of combinatorial chemistry and high-throughput screening allows the identification of many compounds as potential candidate drugs for therapeutic uses. Many potentially valuable drugs, however, are ineffective because they cannot traverse lipid-based barriers, such as cell membranes or intestinal, blood-brain, or placental barriers, or they cannot accumulate at the desirable side of such barriers in concentrations sufficient for therapeutic efficacy.
A drug selection process is needed that detects the physicochemical and pharmacokinetic characteristics of the test compound, i.e., factors that govern the ability of the compound to accumulate in the appropriate compartment. Preferably, such a selection process can be done at an early stage in the drug development process since failure to consider any of these characteristics can lead to significant and costly development problems, delays in getting the product to market, and the failure of the project altogether. This situation is exacerbated by strong pressure for rapid selection of the best candidate drugs for development.
Existing experimental methods for determining the rate and extent at which drugs and similar molecules penetrate physiological barriers are limited, inaccurate, slow, awkward and costly, and they are unsuitable for high throughput screening. Animal models are costly, controversial, labor intensive, and not suited to high-throughput screening. Simple cell culture models and cultured brain capillary endothelial cell and astrocyte models, while in many ways superior to the use of animals, also have various disadvantages, including variability of results and the need for sterile conditions. In addition, the utility of animal models and other in vitro model systems using cells or tissues is often compound-dependent, i.e., they typically require either the use of radioactively labeled test compounds or a spectroscopic detection method whose sensitivity depends on the chromophoric properties of the compounds. The use of radioactively labeled test compounds can introduce further complications resulting from related disposal requirements. These methods can be expensive and time consuming, and are rarely suitable for high-throughput screening programs. Additionally, there is the considerable time and expense of start-up and maintenance of the cell cultures. Although several artificial membrane models have been developed, they also suffer from limitations such as requiring fluorescent test compounds or not employing true lipid bilayers.
Although the rates of penetration of molecules into and through a membrane are ultimately determined by the structural features of the molecules, at present there is no reliable a priori theoretical means to calculate these rates for compounds that are predictive, e.g., for a potential drug, or for more complicated situations where the drug is deposited in a natural carrier molecule, such as serum albumin, or in a synthetic drug delivery vehicle. Thus, there is a need for new compositions and methods for measuring the transport of molecules through lipid barriers.